Here’s an excellent article in Popular Science about the Pioneer anomaly. (Via Dan Vergano on Twitter.) The Pioneer spacecraft, launched in the early 1970’s, have been moseying through the outer regions of the Solar System for quite some time now. But a careful analysis of tracking data indicated that the acceleration of the two spacecraft didn’t quite match what we’d expect from gravity; there appears to be an anomalous acceleration, nearly constant over time and pointing toward the Sun. Many new-physics explanations have been proposed, but it’s always been a difficult scenario to master; it’s very hard to imagine a new force that would account for the Pioneer data but not also show up in observations of the outer planets. (The Voyager spacecraft aren’t as useful for this purpose, as they are guided by tiny thrusters that overwhelm the signal, while the Pioneers float freely and are pointed using gyroscopes.)

The most likely explanation has always been that we didn’t completely understand the spacecraft, or the tracking system. Indeed, it’s been recognized for a while that a small imbalance in how the spacecraft radiated heat could account for the acceleration — but that imbalance didn’t seem to be supported by what we knew about the vessels. That may be changing, however. The Popular Science article is a little cagey, but it mentions a new and unprecedentedly thorough analysis by Viktor Toth and Slava Turshyev that should be coming out soon. Here is as much as they would let on:

Five years have passed. Using the telemetry data, the two scientists created an extremely elaborate “finite element” 3-D computer model of each Pioneer spacecraft, in which the thermal properties of 100,000 positions on their surfaces are independently tracked for the duration of the 30-year mission. Everything there is to know about heat conduction across the spacecraft’s surfaces, as well as the way that heat flow and temperature declined over time as the power of the generators lessened, they know. The results of the telemetry analysis? “The heat recoil force accounts for part of the acceleration,” said Turyshev. They wouldn’t tell me how significant a part. (Turyshev: “We’d like to publish that in the scientific literature.”) But according to Toth, “You can take it to the bank that whatever remains of the anomaly after accounting for that thermal acceleration, it will at most be much less than the canonical value of 8.74 x 10-10 m/s2, and then, mind you, all those wonderful numerical coincidences people talk about are destroyed.”

Doesn’t look good for people who prefer to imagine that wild new physics is responsible. Not that they will go away — the power of wishful thinking is strong. You can already hear them staking out territory, even before the new report comes out:

Other physicists are more combative. “Heat? That’s simply not the right explanation. They are wrong,” commented Johan Masreliez, an independent researcher in Washington who supports the expanding spacetime model of cosmology, for which it is crucial that the value of the Pioneer anomaly equals c times H. “But then I’m biased,” he added.

Even if the new analysis gives a very sensible and believable account of the Pioneer anomaly in terms of very ordinary physics, expect the true believers to hang on for years to come. The rest of us will move on — at least until the next exciting anomaly pops up.

Also: big props to Natalie Wolchover, who wrote the PopSci piece. Very measured tone, carefully researched and well-written.

Big props to Slava Turyshev as well, who was a coauthor on the original anomaly discovery paper and has done amazing work tracking down what could be the cause. Even though, as Dan Fischer notes, the solution has been “obvious,” you have to do the analysis right.

There must be some regime in which GR breaks. It would have been very surprising if the Pioneers were in that regime, so I’m glad Slava put in the effort he’s put in.

eric gisse

The initial rough modeling by Turyshev accounted for roughly 1/3 of the anomaly, from what I remember of the report. Which was several years ago – I did not know Turyshev was still working on this, which is neat.

That thermal modeling wipes out the anomaly comes as no great surprise to me, but does amuse me with how it completely craps all over people who use it to buttress a great many fringe theories.

nicholas suntzeff

Hans Mark has been hinting at this for the last two years. He also said they were going to go back to the original telemetry and re-reduce the data. I don’t think most of us would be surprised that the anomaly was some boring complicated thermal property rather than modified gravity.

psmith

Ah, yet another triumph for the Principle of Sufficient Reason.

Martin

I do like the way that the obligatory-for-balance crackpot ‘supports the expanding spacetime model of cosmology’…

http://commons.bcit.ca/mylife/author/dmcgilvery/ C. Darcy McGilvery

I agree; Natalie Wolchover is great. Can’t wait for her book to come out.

#12 Matt B: It should be Hubble’s constant, which is about 2.5 x 10^-18 s^-1 if one writes it in SI units. Then H*c is roughly equal to 7.5 x 10^-10 m s^-2, which is pretty close to the anomalous acceleration, it seems. It’s some type of numerology. Very often practised by “independent researchers”.

Dunc

the two scientists created an extremely elaborate “finite element” 3-D computer model of each Pioneer spacecraft

And there is the clue as to how they’ll deal with it: “Computer modelling isn’t real science!!!one1!”

http://vixra.org/abs/0907.0018 Peter Fred

“Heat? That’s simply not the right explanation.” If you want to see a $200 experiment that shows that heat is gravitationally attractive go here: http://infralever.blogspot.com/. For a paper and five heat-based experiments that are better controlled and explained go here: http://vixra.org/abs/0907.0018 . If NASA had spent millions of dollars on the five experiments that I performed under my desk for less than $250, they might have gotten the attention that the Pioneer studies have gotten. In addition, others could have performed clones to the experiments that I performed and see if they could also obtain a ~10% average increase of weight of the test mass of four of the experiments that were performed. We have an extragalactic catastrophe which most scientist think of as only a dark matter and dark energy problem. They are not about to question the sacrosanct and inviolable mass-based theories of Newton and Einstein as being the reason why we have this “extragalactic catastrophe.” So go to Amazon.com to get a several copper hemispheres, some ice, a force sensor from Vernier Software and a 1000-watt hot plate from the drug store and see if you can get a million dollars from NASA to fund your under-the-desktop study that shows that spreading infrared radiation is gravitationally attractive.

In the past this would be seen a great clue to a fundamental advance (e.g. perihelion precession of Mercury). The conformal group has been hanging around telling us how important it is for decades, and then it shows up in the solar system, and then those who are intrigued, are called crackpots.

-drl

Chris Winter

Peter Fred wrote (#16): “If NASA had spent millions of dollars on the five experiments that I performed under my desk for less than $250…”

If NASA had spent millions on experiments that you performed for $250 — man, would they have wasted money!

D R Lunsford

All that is needed is a cheap spacecraft with no instruments other than a good radio and computer. It should be spin-stabilized and gyroscopically controlled. It could be done for next to nothing relative to the cost of typical space missions. The IBEX earlier this year showed the value of these cheap experiments when they are well targeted.

-drl

coolstar

good, laborious work by the authors, who came up with the result most of us expected. Which shouldn’t be taken to mean that they shouldn’t have done the work! I think the definition of crackpot includes the fact that no amount of evidence will ever convince them they’re wrong…..

Gus

“The heat recoil force accounts for part of the acceleration,” said Turyshev

Wait a minute, after such a comprehensive analisis telling that heat accounts for part of the acceleration does not in fact confirm the anomaly?

basudeba

The modern theory of gravitation is wrong. Firstly, there is no attractive force as pulling is physically impossible. The so called attraction is the result of entanglement, which implies that gravity is not a single force, but a composite force. We have derived gravitation from electromagnetic interaction and entanglement. It is a composite force of seven. It manifests itself as two forces for macro and micro worlds – both identical in some respects but different in the sense that while the macro manifestation acts between bodies stabilizing the orbits of planets, stars etc. (the proportionality constant being G), the micro manifestation acts within the confinement and regulates structure formation. Thus, the value of G is not constant, but varies from system to system.

However, the derivation as above does not accept extra dimensions, relativity or manipulation of mathematics. In short, it is alternate physics, where each term like reality, time, space, dimension, mass, energy, number, infinity, charge and mathematics etc are precisely defined and only one interpretation applies for these.

basudeba.

doyle featherston

Just wanted to know if it’s possible that the anomaly could be caused in any part by the the “drag” effect of dark matter? Sean, could you please comment? I’m a non-physicist but very curious! Thanks.

http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

Doyle– almost certainly not. Dark matter doesn’t interact noticeably with ordinary matter, or we would have detected it directly long ago.

http://www.groovium.com Moe DeLaun

Apart from the disputatious nature of *every* darned topic these days (we do agree the Sun appears to rise in the East, right?), it may be that Nature ultimately splits the difference. Science’s long-term effort to isolate variables through rigorous measurement and analysis will account for much that is odd, yet that same rigorous study will reveal real phenomena that require adjustments in our understanding.

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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson.
Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .